The main objective of the proposed research is to describe how we perceive and remember auditory information. The research is carried out in the framework of a human information processing model which assumes that there is a sequence of processing stages between stimulus and response. The auditory recognition of speech and nonspeech sounds is studied in a backward recognition masking paradigm. In this task, a test sound is presented followed after some silent period by a masking sound. The test and masking sounds are presented at a normal listening intensity. The masking sound interferes with the recognition of the test sound if it occurs before its recognition is complete. The paradigm can be used to discover the properties of a preperceptual auditory storage which outlasts the stimulus presentation. One goal is to determine what sounds function as perceptual units in speech perception. The backward masking paradigm can be used to determine the size of perceptual units in speech and to what extent syntactic and semantic context operate in the initial stage of speech perception.